When school administrators started screaming "code red, get back in the building", Lewis and his classmates ran back to their classroom with their teacher where they "huddled under the desks" before moving into a storage cupboard.

"We didn't hear the bullets, but we heard the helicopters," he said. "We knew at that point it was something really serious."

The high school student said he and his classmates "were all on our phones" as they hid.

"I had people standing next to me watching CNN live trying to figure out what's going on," he said.

"It's one of those things you see on the news and think that will never happen to you, but it has.

"I have friends who have been killed, I have friends who have been shot. How can this be real?"